Disc filter pre-screen dual media disc filter

ABSTRACT

According to various aspects and embodiments, a system and method for two-stage filtration is provided. The system includes an inlet fluidly connectable with wastewater, a first stage filter assembly that is fluidly connectable with the inlet and has a rotary drum with a filter surface configured for radially inward fluid flow, a second stage filter assembly that is fluidly connectable with the first stage filter and has a plurality of filter discs configured for radially outward fluid flow, and an outlet fluidly connectable with filtrate generated by the second stage disc filter assembly.

RELATED APPLICATIONS

This application claims priority under 35 U.S.C. § 119(e) to U.S.Provisional Application Ser. No. 62/374,097, titled “DISC FILTERPRE-SCREEN DUAL MEDIA DISC FILTER,” filed on Aug. 12, 2016, which isherein incorporated by reference in its entirety.

BACKGROUND Technical Field

The technical field relates generally to wastewater treatment processes,and more particularly, to media filtration in wastewater treatmentprocesses.

Background Discussion

Water filtration processes typically include primary, secondary, andtertiary processes to treat wastewater to remove contaminants, such assuspended solids, biodegradable organics, phosphorous, nitrogen,microbiological contaminants, and the like, to provide a clean effluent.

The first or primary treatment process typically involves mechanicallyseparating large solids and other suspended matter in the wastewaterfrom the less dense solids and liquid in the wastewater. Primarytreatment processes are typically done in sedimentation tanks usinggravity and provide a primary effluent.

Secondary treatment typically includes biological treatment of theprimary effluent. The biological treatment units or vessels used forsecondary treatment typically include bacteria that break downcomponents of the wastewater, such as organic components. The biologicaltreatment processes in the biological treatment units or vessels mayreduce the total organic content and/or biochemical oxygen demand of thewastewater. This is typically done by promoting the consumption of thecarbonaceous and nutrient material by bacteria and other types ofbeneficial organisms already present in the wastewater or mixed into thewastewater.

Tertiary processes typically involve removing suspended solids and anyremaining contaminants or pollutants from the wastewater so that theremaining water can be either reused or disposed of safely in theenvironment. Tertiary processes can include filtration and/or theaddition of any one or more of chemicals, UV light, and ozone.

Many wastewater treatment plants utilize a disc filter system to filterwater. Such systems typically include a plurality of discs that eachcomprise a plurality of filter segments. Each filter segment includes apair of filter panels which are spaced apart and arranged on an outersurface of a central drum. A cap is attached to the top of each pair offilter panels to form a pocket shaped filter segment for receivingwater. Each filter panel includes filter media, such as finely wovencloth, for filtering water.

Each filter panel is attached to the drum by a filter supportarrangement. Each filter support includes a plurality of supportopenings which provide fluid communication between adjacent filtersegments. This enables water and air to flow circumferentially betweenadjacent filter segments as the drum rotates.

In operation, the drum is rotated and the water to be filtered isintroduced into the drum. The water then exits through ducts in the drumand flows into filter segments inside the filter support. The water inthe filter support is then filtered through the media of the filterpanels to provide filtered water. The filtered water is then collectedin a chamber and exits the disc filter through an effluent pipe.Particulates which are filtered out by the filter panels remain withinthe filter segments on the inside surface of the filter media of thefilter panels. A spray device is used to spray the panels with water todislodge the particulates and clean the filter media. The particulatesare then collected onto a trough and removed from the disc filtersystem.

Openings in the central drum that function to provide a passageway forthe water to be transferred into the interior of the filter discs aretypically larger than the openings of the filter media on the filterpanels. Influent wastewater having high Total Suspended Solids (TTS)levels will therefore clog the filter media more quickly, which reducesthroughput.

Furthermore, objects in the wastewater, such as rags and other largeobjects may flow through the openings in the drum into the interior ofthe filter panels and become trapped. This results in the loss ofeffective filter panel filtration area and thus a loss of efficiency.For example, in order to remove these large objects, the disc filter hasto be taken offline and the filter panels have to be removed andcleaned, which is both labor intensive and time consuming.

SUMMARY

Aspects and embodiments are directed to a two-stage filtration systemfor filtering wastewater that includes a first stage filter assemblythat is disposed sequentially to and upstream from a second stage filterassembly.

According to an aspect of the present disclosure, a filter device forfiltering wastewater is provided. The filter device comprises a drumfilter including a rotary drum with a filter surface having a first sidefacing an interior of the drum and a second side facing an exterior ofthe rotary drum and being fluidly connectable with a source ofwastewater, and a disc filter having an inlet fluidly connectable withthe first side of the filter surface of the rotary drum.

In some embodiments, the disc filter includes a plurality of disc-shapedfilter members attached to a central drum that are configured to receivefiltered wastewater passed through the filter surface of the drum filterand to filter the filtered wastewater. In one embodiment, the inlet ofthe disc filter is fluidly connectable with an interior of the centraldrum of the disc filter. In another embodiment, the rotary drum of thedrum filter and the central drum of the disc filter are positioned alonga common longitudinal axis. In some embodiments, the rotary drum of thedrum filter is coupled to the central drum of the disc filter.

According to a another embodiment, the disc filter further comprises ahousing that at least partially surrounds the drum filter and the discfilter, the housing having an inlet trough fluidly connectable with thewastewater and the second side of the filter surface of the rotary drumfilter, an outlet trough fluidly connectable with filtrate, and asealing plate configured to separate the inlet trough from the outlettrough.

In some embodiments, the disc filter further comprises a drum filtercollection trough fluidly connectable with the exterior of the rotarydrum.

In some embodiments, the disc filter further comprises a backwashingsystem. According to one embodiment, the backwashing system comprises afirst plurality of spray nozzles configured to spray filtrate onto theplurality of disc-shaped filter members, a disc filter backwash troughconfigured to collect backwashed filtrate from the plurality ofdisc-shaped filter members, and a second plurality of spray nozzlesconfigured to spray filtrate onto the first side of the filter surfaceof the rotary drum, wherein the drum filter collection trough isconfigured to collect backwash from the filter surface of the rotarydrum.

According to at least one embodiment, the filter surface of the rotarydrum is configured to retain solids on the second side while permittingthe wastewater to filter through the filter material to the first sideof the filter material and the interior of the rotary drum as filteredwastewater. In some embodiments, the filter surface of the drum filterhas openings with a diameter in a range of about 20 microns to about 800microns. According to certain embodiments, the filter surface of thedrum filter comprises one of wedge wire screen material or woven filtermedia material. In one embodiment, the plurality of disc-shaped filtermembers include a filter media with openings having a diameter in arange of about 6 microns to about 300 microns.

According to some embodiments, the wastewater is from one of a secondaryor primary treatment process.

According to another aspect of the present disclosure, a two-stagefiltration system for filtering wastewater is provided that includes aninlet fluidly connectable with the wastewater, a first stage filterassembly fluidly connectable with the inlet and having a rotary drumwith a filter surface configured for radially inward fluid flow, asecond stage filter assembly fluidly connectable with the first stagefilter assembly and having a plurality of filter discs configured forradially outward fluid flow, and an outlet fluidly connectable withfiltrate generated by the second stage filter assembly.

In some embodiments, the plurality of filter discs are attached to acentral drum that is fluidly connectable with an interior of the rotarydrum of the first stage filter assembly.

According to at least one embodiment, the first stage filter assemblyand the second stage filter assembly are rotatable around a commonlongitudinal axis, and the system further comprises a drive assemblycoupled to the first stage filter assembly and the second stage filterassembly. In another embodiment, the two-stage filtration system furtherincludes a backwashing system having a first plurality of spray nozzlesconfigured to spray the filtrate onto the plurality of filter discs anda second plurality of spray nozzles configured to spray the filtrateonto an inwardly facing side of the filter surface of the rotary drum.

In another embodiment, the two-stage filtration system further includesa level sensor configured to provide measurements of a level ofwastewater provided by the inlet to the first stage filter assembly. Ina further embodiment, the two-stage filtration system further includes acontroller operatively coupled to the level sensor, the drive assembly,and the backwashing system, the controller configured to control atleast one of the drive assembly and the backwashing system based onmeasurements from the level sensor. In some embodiments, the filtersurface of the drum filter has openings with a diameter in a range ofabout 20 microns to about 800 microns. In some embodiments, the filterdiscs include a filter media with openings having a diameter in a rangeof about 6 microns to about 300 microns.

In some embodiments, the inlet of the two-stage filtration system isfluidly connectable with a secondary clarifier of a secondary treatmentprocess. In other embodiments, the inlet is fluidly connectable withinfluent to a primary treatment process.

According to one embodiment, the second stage disc filter assemblyincludes a central drum configured to receive filtered wastewater fromthe first stage filter assembly, the central drum including a pluralityof drum apertures, a frame comprising a plurality of frame supports eachhaving an attachment portion coupled to the central drum and a radialstrut portion extending from the attachment portion, each of theplurality of frame supports defining a single frame aperture thatextends through the attachment portion and along an entire length of theradial strut portion to correspond with the shape of the frame support,and a plurality of adjacent filter segments positioned around thecentral drum, each of the plurality of adjacent filter segments defininga cavity in fluid communication with at least one of the plurality ofdrum apertures and supported at a first side by a first frame supportand at a second side by a second frame support, the plurality of frameapertures and cavities arranged to form a circumferential open fluidchannel extending continuously around the central drum to enable thefiltered wastewater to pass substantially unimpeded through theplurality of drum apertures and through the plurality of adjacent filtersegments. In some embodiments, the single frame aperture forms aninverted substantially T-shaped configuration.

According to another aspect of the present disclosure, a method oftreating wastewater is provided. The method includes introducing thewastewater to a first-stage filtration operation comprising a barrierfilter to produce filtered wastewater, and introducing the filteredwastewater to a second-stage filtration operation comprising a discfilter to produce treated water.

In some embodiments, the method further includes measuring a level ofthe wastewater introduced to the barrier filter of the first stagefiltration operation. In another embodiment, the method further includesbackwashing a filter surface of the barrier filter based on the measuredlevel of wastewater. In some embodiments, the barrier filter comprises arotary drum configured for radially inward fluid flow. In someembodiments, the disc filter is configured for radially outward fluidflow.

Still other aspects, embodiments, and advantages of these exampleaspects and embodiments, are discussed in detail below. Moreover, it isto be understood that both the foregoing information and the followingdetailed description are merely illustrative examples of various aspectsand embodiments, and are intended to provide an overview or frameworkfor understanding the nature and character of the claimed aspects andembodiments. Embodiments disclosed herein may be combined with otherembodiments, and references to “an embodiment,” “an example,” “someembodiments,” “some examples,” “an alternate embodiment,” “variousembodiments,” “one embodiment,” “at least one embodiment,” “this andother embodiments,” “certain embodiments,” or the like are notnecessarily mutually exclusive and are intended to indicate that aparticular feature, structure, or characteristic described may beincluded in at least one embodiment. The appearances of such termsherein are not necessarily all referring to the same embodiment.

BRIEF DESCRIPTION OF DRAWINGS

Various aspects of at least one embodiment are discussed below withreference to the accompanying figures, which are not intended to bedrawn to scale. The figures are included to provide an illustration anda further understanding of the various aspects and embodiments, and areincorporated in and constitute a part of this specification, but are notintended as a definition of the limits of any particular embodiment. Thedrawings, together with the remainder of the specification, serve toexplain principles and operations of the described and claimed aspectsand embodiments. For purposes of clarity, not every component may belabeled in every figure. In the figures:

FIG. 1A is a partial cut-away perspective view of a disc filter inaccordance with one or more aspects of the invention;

FIG. 1B is a cross-sectional side view of the disc filter of FIG. 1Ataken along section line 1B;

FIG. 2A is a perspective view of a drum typically used in the discfilter of FIGS. 1A and 1B;

FIG. 2B is a side view of the drum of FIG. 2A;

FIG. 3 is a side view of a portion of a disc filter;

FIG. 4A is a front view of a filter panel in a support frame attached toa central drum in a disc filter;

FIG. 4B is a perspective view of the filter panel of FIG. 4A;

FIG. 4C is a side view of the filter panel of FIG. 4A with a portion ofa support structure removed;

FIG. 5A is a perspective view of two-stage filtration system inaccordance with one or more aspects of the invention;

FIG. 5B is a cross-sectional side view of a two-stage filtration systemin accordance with one or more aspects of the invention;

FIG. 6A is a side schematic view of a drum filter in accordance with oneor more aspects of the invention;

FIG. 6B is an enlarged view of the circled portion (labeled “6B”) ofFIG. 5A;

FIG. 6C is a photograph of a drum filter attached to a disc filter inaccordance with one or more aspects of the invention;

FIG. 7A is a schematic front view of a drum filter in accordance withone or more aspects of the invention;

FIG. 7B is an enlarged view of the circled portion (labeled “7B”) ofFIG. 7A;

FIG. 8 is a partial perspective view of a top portion of a drum filterin accordance with one or more aspects of the invention;

FIG. 9 is a photograph of a drum filter attached to a disc filter inaccordance with one or more aspects of the invention;

FIG. 10 is a schematic flow diagram of a wastewater treatment processthat includes a two-stage filtration system in accordance with one ormore aspects of the invention;

FIG. 11 is a schematic view of a backwash system in accordance with oneor more aspects of the invention;

FIG. 12A is a perspective view of a frame support;

FIG. 12B is a perspective view of the frame support shown in FIG. 12Aattached to a central drum;

FIG. 12C is an end view of the frame support of FIG. 12A attached to acentral drum;

FIG. 12D is a side view of a filter disc including several filter panelsand frame supports;

FIG. 12E is a perspective view of a filter disc including a number offilter panels;

FIG. 13 is a schematic diagram of a two-stage filtration system;

FIG. 14 is a schematic of a pilot plant used in accordance with one ormore aspects of the invention;

FIG. 15 is a schematic flow diagram of a test site and placement of thepilot plant of FIG. 14;

FIG. 16 is a graph showing results of one test performed using atwo-stage filtration system in accordance with one or more aspects ofthe invention;

FIG. 17 is a graph showing results of another test performed using atwo-stage filtration system in accordance with one or more aspects ofthe invention;

FIG. 18A is a graph showing results of another test performed using atwo-stage filtration system in accordance with one or more aspects ofthe invention; and

FIG. 18B is a graph showing results of another test performed using atwo-stage filtration system in accordance with one or more aspects ofthe invention.

DETAILED DESCRIPTION

The aspects disclosed herein in accordance with the present invention,are not limited in their application to the details of construction andthe arrangement of components set forth in the following description orillustrated in the accompanying drawings. These aspects are capable ofassuming other embodiments and of being practiced or of being carriedout in various ways. Examples of specific implementations are providedherein for illustrative purposes only and are not intended to belimiting. In particular, acts, components, elements, and featuresdiscussed in connection with any one or more embodiments are notintended to be excluded from a similar role in any other embodiments.For example, the teachings of this invention apply not only to an“outside-in” type drum filter connected to an “inside-out” disc filter,but also apply to other types of filter configurations, including an“inside-out” type drum filter connected to an “outside-in” disc filter.

Also, the phraseology and terminology used herein is for the purpose ofdescription and should not be regarded as limiting. Any references toexamples, embodiments, components, elements or acts of the systems andmethods herein referred to in the singular may also embrace embodimentsincluding a plurality, and any references in plural to any embodiment,component, element or act herein may also embrace embodiments includingonly a singularity. References in the singular or plural form are notintended to limit the presently disclosed systems or methods, theircomponents, acts, or elements. The use herein of “including,”“comprising,” “having,” “containing,” “involving,” and variationsthereof is meant to encompass the items listed thereafter andequivalents thereof as well as additional items. References to “or” maybe construed as inclusive so that any terms described using “or” mayindicate any of a single, more than one, and all of the described terms.In addition, in the event of inconsistent usages of terms between thisdocument and documents incorporated herein by reference, the term usagein the incorporated reference is supplementary to that of this document;for irreconcilable inconsistencies, the term usage in this documentcontrols.

While the invention illustrated herein is described as being employed ina wastewater treatment setting, and particularly as a tertiary treatmentsystem, other uses and arrangements are possible. For example, theinvention may be used as a primary wastewater treatment system. Otherwastewater treatment applications include use as a secondary clarifierin a municipal wastewater treatment plant. In addition to wastewatertreatment uses, the present invention can also be used for filteringwater used in industrial and manufacturing processes, such as wood,paper, and food industries, as well as production facilities.

As discussed above, rotary disc filters may be used to remove suspendedsolids from water. Examples of suitable disc filters that may be used inaccordance with aspects of the invention are discussed in PCTApplication Nos. PCT/US2007/017847 and PCT/US2008/008671, each of whichis incorporated herein by reference in its entirety. FIGS. 1A and 1Billustrate a possible rotary disc filter 115, also referred to herein assimply a “disc filter” or “disc filter assembly.” Suitable examples ofdisc filters for use with the invention include the Forty-X™ discfilters manufactured by Evoqua Water Technologies, although other discfilters may be used.

The disc filter 115 configuration shown in FIGS. 1A and 1B employs afilter media 118 that is pleated filter media. The filter media 118 maybe woven or non-woven. In addition, pile cloth, needle felt,microfiltration, nanofiltration, reverse osmosis, or other membranes maybe employed as media constructions. Non-limiting examples of materialsfor use in making filter media include polyester, metal-coatedpolyester, antimicrobial-coated polyester, polypropylene, nylon,stainless steel wire, glass fiber, alumina fiber, glass filledpolypropylene (e.g., 17%), glass-filled acetal, glass-filled nylon, orany combination thereof. It should also be noted that the term “filtermedia” should be interpreted broadly to cover any component that filtersa fluid. Other terms included within the definition of filter mediainclude membrane, element, filter device, and the like. As such, theterm “filter media” should not be narrowly interpreted to exclude anycomponent that filters fluid.

Referring back to FIGS. 1A and 1B, disc filter 115 comprises a housing125, such as a metal tank that substantially encloses a central drum 119that is configured to rotate and supports a plurality of disc-shapedfilter members or filter discs 117. It will be appreciated thatvariations on this design, including those employing a frame intended tofacilitate mounting of the unit in a concrete tank, may also be used.

The disc filter 115 also includes a drive assembly 170. The driveassembly 170 includes at least two bearings that support the centraldrum 119 for rotation. A driven sprocket 50 is coupled to the centraldrum 119 and a drive sprocket 45 is coupled to a motor 55 or other primemover. In the illustrated construction, a belt engages the drivesprocket 45 and the driven sprocket 50 such that rotation of the motor55 produces a corresponding rotation of the central drum 119. Inpreferred constructions, the sprockets 45, 50 are sized to produce asignificant speed reduction. However, some constructions may employ aslow speed drive with no speed reduction if desired. While theillustrated construction employs a belt drive, other constructions mayemploy gears, shafts, chains, direct drive, or other means fortransferring the rotation of the motor 55 to the central drum 119.

The disc filter 115 also includes an influent pipe 155 (also referred toherein as an inlet to the housing) that directs influent into aninterior 65 (see FIG. 4A) of the central drum 119, an effluent pipe 160(also referred to herein as an outlet to the housing) that directsfiltered fluid from an outlet trough or chamber 135 defined within thehousing 125 out of the disc filter 115. The disc filter 115 may alsoinclude a spray water pipe 80 that provides high-pressure water to aplurality of spray nozzles 147 (see FIG. 11) that is periodically usedto clean the filter media 118. A backwash pipe 90 transports the spraywater after use and directs it out of the disc filter 115.

The spray bars 190 may be positioned between adjacent filter discs 117and at the ends of the disc filter 115 to enable the spraying ofhigh-pressure water in a reverse flow direction through the pleatedfilter media 118 to provide backwashing of the filter media 118. Becausethe filter media 118 is pleated and thus angled with respect to theplane of the filter discs 117, the use of nozzles (147) that aresimilarly angled may provide for more efficient backwash cycles. Thus,the nozzles are angled approximately 45 degrees off of a normaldirection to the planes of the filter discs 117. In addition, twonozzles may be provided at each spray point, with the nozzles angledwith respect to one another at about 90 degrees such that both sides ofthe pleats are sprayed directly during the backwashing. In someinstances, a straight on direct spray may be utilized. In addition,bouncing spray off the filter media at an angle improves the cleaningeffect and efficiency for a given amount of backwash flow and sprayvelocity.

The disc filter 115 of FIGS. 1A and 1B employs a plurality of filterdiscs 117 to increase the overall filter area. The number and size ofthe filter discs 117 can be varied depending on the flow requirements ofthe system. For example, additional filter discs 117 can be attached tothe central drum 119 to increase the capacity of the disc filter 115without having to pass additional flow through any of the alreadyexisting filter discs 117. According to various embodiments, the discfilter 115 is configured as an “inside-out” configuration, meaning thatwater to be filtered enters the central drum 119 and flows from thecentral drum 119 into the filter discs 117, and from there outwardlythrough the filter media 118, as described further below. This type ofconfiguration may also be referred to herein as radially outward fluidflow.

FIGS. 2A and 2B illustrate a possible central drum 119 configurationthat may be used in accordance with one or more embodiments. The centraldrum 119 includes an outer surface 95 and two end surfaces 156 thatcooperate to define an interior space. One end is open to permit flowand the other end is sealed against flow. Several drum apertures 158 arearranged in a series of axial rows with each row including a number ofdrum apertures 158 that extend circumferentially around a portion of theouter surface 95. The drum apertures 158 are rectangular although it isunderstood that other shapes may be suitable. Attachment apertures 159are positioned on either side of each drum aperture 156. Each drumaperture 158 is associated with a set of attachment apertures 159. Asillustrated in FIG. 2A, the outer surface 95 of the central drum 119includes a number of flat planar surfaces that contact one another todefine a polygonal cross section. It is to be appreciated that acircular cross section or a cylindrical or other shape is also withinthe scope of this disclosure.

Referring to FIG. 3, a side view of one of the filter discs 117 of FIGS.1A and 1B is shown. Each filter disc 117 includes a plurality of filterpanel sets 300. Each filter panel set 300 includes two associated filterpanels 116. In FIG. 3, one of the filter panels 116 from each panel set300 is shown. The filter disc 117 in FIG. 3 depicts twelve filter panels116 and thus filter disc 117 includes a total of twenty four filterpanels 116. However, it is to be appreciated that other constructionsmay employ more or fewer filter panels 116 as desired.

After filtering, and during rotation of the central drum 119, the filterpanels 116 exit the liquid and pass the spray bars 190. During abackwash cycle, spray nozzles 147 (see FIG. 11) are used to spray thefilter panels 116 with high-pressure water or chemicals to dislodge theparticulates and clean the filter media 118 as the central drum 119rotates. The water droplet impact vibration and penetration of thefilter media 118 by a portion of the water removes debris that is caughton the upstream surface of the pleated filter media 118. The debris andwater are collected in the trough 142 and transported out of the discfilter 115 by backwash pipe 90.

FIGS. 4A and 4B illustrate possible arrangements of the filter panels116. FIG. 4A illustrates the panel 116 mounted in the support structure121. FIG. 4B illustrates a pleated panel. The filter panels 116 includea pleated filter media 118, a perimeter frame 210, and several supportgussets or stringers 215. In some constructions, the stringers 215 aremolded as an integral part of the frame 210 with other attachment meansalso being suitable for use. In some constructions, the pleated filtermedia 118 is formed from a single piece of material that is sized andshaped to fit within the perimeter frame 210. In the illustratedconstructions, the pleats extend in a substantially radial directionwith other orientations also being possible. In one construction, astainless steel screen is employed as the filter media 118. Otherconstructions may employ woven polyester, cloth, or other materials. Thematerials used and the size of the openings (also referred to herein aspore size) are chosen based on the likely contaminates in the effluent,the flow rate of the effluent, as well as other factors. In oneembodiment, the openings are in a range of 10 and 30 microns indiameter. Smaller and larger openings are also within the scope of thisdisclosure. For example, in some applications, the filter media may haveopenings that are in a range of 6 to 300 microns in diameter. Accordingto another example, the filter media has openings that are about 100,150, or 200 microns in diameter. As indicated in the examples discussedbelow, according to some embodiments, the filtrate 122 generated by thedisc filter may have a TSS concentration of less than 5 mg/L.

As illustrated in FIG. 4B, one construction of the frame 210 is formedwith a cross section of an angled member that includes a flow-parallelleg 230 and a flow-transverse leg 235. The flow-transverse leg 235receives the respective inner diameter seal 165 as illustrated in FIG.4C, and provides additional stiffness to the flow-parallel legs 230. Theflow-parallel legs 230 are sized to substantially match the peak-to-peakheight of the pleated filter media 118. The frame 210 also includes twosubstantially parallel sides 236 and two non-parallel sides 237 that arearranged such that they are substantially radial with respect to thecentral drum 119.

Referring to FIG. 4C, one of the filter panel sets 300 is shown. FIG. 4Cis a side view of FIG. 4A with a right portion of a support structure121 (see FIG. 4A) removed. The filter panels 116 are mounted in thesupport structure 121 such that the filter panels are spaced apart fromeach other. An attachment plate 123 having an aperture 146 engages theattachment apertures 159 around a drum aperture 158 to attach thesupport structure 121 to the central drum 119. A cap 175 is located overa top portion of the filter panels 116. The filter panels 116, thesupport structure 121 in which they are mounted, the cap 175, and theattachment plate 123 define a partially enclosed space 180. Thepartially enclosed space 180 extends circumferentially around thecentral drum 119 through each filter panel set 300 on the filter disc117. Fluid is able to pass from within the central drum 119, through thedrum aperture 158 and aperture 146 in the attachment plate 123 and intothe enclosed space 180 to enable fluid to flow circumferentially withineach filter panel set in the filter disc 117. A perimeter seal 165 islocated on a perimeter 161 of each filter panel 116 and serves toinhibit leakage of water from around the filter panel 116.

Referring to FIG. 1B in conjunction with FIG. 3, the spray water pipe 80extends the full length of the disc filter 115 and defines adistribution manifold 185. A spray bar 190 is positioned betweenadjacent filter discs 117 and at each end of the disc filter 115. Adistribution pipe 195 extends between the manifold 185 and the spray bar190 to provide for fluid communication of high-pressure water to thespray bar 190. The spray bar 190 includes nozzles that spray water ontothe filter panels 116 to periodically clean the filter panels 116 asdescribed in greater detail below with reference to FIG. 11.

A disc filter backwash trough 142 is positioned beneath the spray bar190 between adjacent filter discs 117 to catch the spray water orbackwash, including any particulate matter removed from the filterpanels 116. The backwash and particles are then removed from the discfilter 115 via the backwash pipe 90.

As mentioned above, openings in the central drum 119 (e.g., apertures158) provide a passageway for water to be sent into the interior of thefilter panels (e.g., enclosed space 180). Since the openings or poresize of the filter media 118 is smaller than these openings, solids thatare larger than the pore size opening become attached to the filtermedia. In addition, larger objects such as rags can also flow throughthe drum openings and become trapped in the interior of the filterpanels, which not only reduces filter panel filtration area but alsodecreases efficiency since the disc filter has to be taken offline toremove these larger trapped objects since the backwash process isineffective at removing such large objects.

In accordance with one or more embodiments, a two-stage filtrationsystem for filtering wastewater is provided that addresses the problemsdiscussed above related to the trapped solids. The two-stage filtrationsystem includes a drum filter, also referred to herein as a “barrierfilter” that functions as a first stage filtration process that ispositioned upstream from a disc filter that functions as a second stagefiltration process. The drum filter functions as a preceding filter or apre-filter which provides a certain degree of filtering to a secondstage filtration process such as the disc filter. For instance, the drumfilter may be configured to remove material that is larger than 100microns, including large debris from plant upsets caused by stormsurges, etc. The drum filter may be directly attached to the disc filtersuch that the drum filter acts as an extension of the disc filter andfunctions to protect the disc filter from large debris and foreignobjects. Influent wastewater passes through the drum filter first, as afirst stage filtration operation. The drum filter removes largerparticulates and generates filtered wastewater that is then directedthrough the disc filter. The disc filter functions as a second statefiltration operation by removing finer particulates from the filteredwastewater that passed through the drum filter to generate filtrate.

FIG. 5A is a perspective view of one embodiment of a two-stagefiltration system 100, also referred to herein as a “filter device.” Thefilter device 100 includes a drum filter 105, also referred to herein asa “first stage filter assembly” or a “first stage drum filter assembly,”and a disc filter 115, also referred to herein as a “second stage filterassembly” or a “second stage disc filter assembly.” The drum filter 105includes a rotary drum 110 and the disc filter 115 includes a centraldrum 119. The rotary drum 110 and the central drum 119 are positionedalong a common longitudinal axis 120. The drum filter 105 and the discfilter 115 are disposed within a housing 125 that at least partiallysurrounds the drum filter 105 and the disc filter 115. The configurationshown in FIG. 5A has a front panel of the housing 125 that is removed toshow the drum filter 105 and other features of the filtration system100. Referring back to the disc filter 115 FIG. 1B, the drum filter 105may be positioned in the space defined by the inlet trough 130 of thehousing 125.

FIG. 5B is a side view of a two-stage filtration system 100. The housing125 includes an inlet 155 for receiving wastewater 102 to be filteredthat collects in an inlet trough 130 that is in fluid communication orotherwise fluidly connectable with the rotary drum 110 of the drumfilter 105. As discussed in further detail below, the wastewater 102passes through the filter surface 112 of the drum filter 105 as filteredwastewater 104. The filtered wastewater 104 that has been filtered bythe drum filter 105 enters one or more openings 150 in the central drum119 of the disc filter 115 to the interior of the central drum 119 whereit is then transferred to the filter discs 117 of the disc filter 115.The filtered wastewater 104 then passes through the filter media 118 ofthe filter discs 117 and collects in an outlet trough 135 of the housing125 as filtrate 122. An outlet 160 of the housing 125 allows forfiltrate 122 to exit the system. The two-stage filtration system 100 mayalso include a sealing plate 126 that is configured to separate theinlet trough 130 from the outlet trough 135 and a drive assembly 170that functions to rotate the rotary drum 110 of the drum filter 105 andthe central drum 119 of the disc filter 115.

The housing 125 includes an inlet 155 that is in fluid communication orotherwise fluidly connectable with wastewater to be filtered 102. Thewastewater to be filtered 102 may be piped to the inlet from any one ofa number of various sources. In some embodiments, the wastewater 102 isfrom a previous wastewater treatment process, including any one of aprimary, secondary, or tertiary treatment process. According to oneembodiment, the wastewater 102 is from a secondary treatment process,and the two-stage filtration system 100 may function as at least aportion of a tertiary treatment process. For example, the wastewater 102may be sourced from a secondary clarifier of a secondary treatmentprocess, as shown in FIG. 10. According to other embodiments, thewastewater 102 may be influent to a primary treatment system (i.e.,“wastewater influent” in FIG. 10), and the two-stage filtration system100 may function as at least a portion of a primary treatment process.

According to some embodiments, the wastewater 102 has a concentration oftotal suspended solids (TSS), also referred to herein as simply“suspended solids” in a range of approximately 10-30 mg/L. In otherembodiments, the wastewater 102 has a TSS concentration that is greaterthan 30 mg/L, for example, in primary filtration applications and ininstances where the wastewater 102 includes storm water runoff oreffluent from a clarifier “burping” process, the wastewater 102 may havea concentration in a range of approximately 100-500 mg/L.

The drum filter 105 includes a rotary drum 110 with a filter surface 112that has a first side 114 a that faces an interior of the rotary drum110 and a second side 114 b that faces an exterior of the rotary drum.According to the embodiments discussed herein, the drum filter 105 isconfigured as an “outside-in” filter, such that wastewater to befiltered 102 (see FIG. 6A) is passed through the filter surface 112 fromthe second side 114 b (exterior of the rotary drum) to the first side114 a (interior of the rotary drum) to generate a filtered wastewater.This type of configuration may also be referred to herein as radiallyinward fluid flow.

The filter surface 112 of the rotary drum 110 may be any one of a numberof different types of filtration media that have openings or pores thatallow water to pass through the filter surface but retain solids orother undesirable substances. The size of the openings may depend on thecharacteristics of the incoming wastewater 102 and/or the type of filtersurface 112 used. In some embodiments, the filter surface 112 hasopenings that are in a range of approximately 1-1000 microns indiameter, and according to one embodiment, the openings in the filtersurface 112 have a diameter that is in a range of approximately 20-800microns, although smaller and larger sized openings for the filtersurface of the drum filter are within the scope of this disclosure.

The filter surface 112 may be constructed from any corrosion resistantmetal material. In some embodiments, the filter surface 112 is a metalmesh material. Non-limiting examples of metal mesh material includestainless steel, nickel alloys, other metal alloys, brass, bronze,titanium, or any combination thereof. In one embodiment, the filtersurface 112 is a wedge wire screen material. In other embodiments, thefilter surface 112 is a polymer material. In some embodiments, thefilter surface 112 is a woven filter media material.

FIG. 6A shows one example of a filtration operation using the drumfilter 105. Wastewater to be filtered 102 enters the inlet trough 130 ofthe housing 125 through the inlet 155. At least a portion of the rotarydrum 110 rests in the wastewater 102. For example, in accordance withone embodiment, a portion of the drum area remains above the water level(see example shown in FIG. 7B indicated a maximum water level) forpurposes of accommodating spray nozzles (discussed below and refer toFIGS. 7A and 7B) that spray the filter surface 112 of the rotary drum110 from the inside out. However, as will be appreciated, according toother designs, the rotary drum 110 may be fully immersed in thewastewater 102. This type of configuration may be useful for removingfloatable materials entrained within the wastewater 102.

Referring back to FIG. 6A, at least a portion of the second side 114 bof the filter surface 112 is in fluid communication or otherwise fluidlyconnectable with the wastewater 102. During operation, the driveassembly 170 applies a driving force to the rotary drum 110 to rotatethe rotary drum 110 through the wastewater 102. As shown by the arrow inFIG. 6A, the configuration of the drum filter 105 of FIG. 6A indicatesthat the rotary drum rotates in a counter-clockwise direction, althoughit is to be appreciated that clockwise rotation is also within the scopeof this disclosure.

According to one embodiment, the wastewater 102 flows through the secondside 114 b of the filter surface 112 to the first side 114 a as filteredwastewater 104. Wastewater 102 is forced through the filter surface 112of the rotary drum 110 by a pressure differential caused by a differencein water height between a high pressure source (water at a higher level)on the outside of the rotary drum 110 (i.e., the presence of thewastewater 102 in the inlet trough 130 that the rotary drum 110 is atleast partially immersed in) and the inside of the rotary drum 110,which is at a lower pressure (and lower height water level). The highpressure source on the outside of the rotary drum 110 pushes thewastewater 102 through the filter surface 112 to the inner chamber ofthe rotary drum 110. The filtered wastewater 104 then flows through oneor more openings 150 in the central drum 119 of the disc filter viagravitational forces (see arrows in FIG. 6A). The openings 150 maytherefore function as an inlet to the disc filter 119, including theinterior of the central drum 119. Referring to the photograph shown inFIG. 6C, a flange 152 or other attachment mechanism may be used toattach the rotary drum 110 of the drum filter 105 to the central drum119 of the disc filter 115. In some embodiments, the openings 150 in thecentral drum 119 may be slots, such as those shown in FIG. 6C. Thefiltered wastewater 102 passes through the openings 150 in the centraldrum 119 where it is then transferred to the filter discs 117.

Solids 106 too large to pass through the openings in the filter surface112 adhere to the exterior (second side 114 b) of the filter surface112. A doctor blade 162 or other scraping device functions to scrape offor otherwise remove the filtered-out solid substances 106 from the fromthe second side 114 b of the filter surface 112 as the rotary drum 110rotates, which is shown in FIG. 6B. For instance, a scraping edge of thedoctor blade 162 rests against the outer surface of the rotary drum 110and scrapes the solids 106 off of the outer surface of the filtersurface 112 as the rotary drum 110 rotates. The scraped solids 106 passalong a top surface of the doctor blade 162, for example, by the forceof gravity, and are collected in a drum filter collection trough 140,which is shown in FIGS. 5A, 6B, 7A, and 7B. The drum filter collectiontrough 140 is therefore in fluid communication or otherwise fluidlyconnectable with the exterior of the rotary drum 110. A portion of thedrum filter collection trough 140 may be at least partially enclosed byan enclosure 141 (see FIG. 6B) that helps confine the solids 106 anddirect them to the collection trough 140. The doctor blade 162 may bemounted to an internal portion of the enclosure 141 and may bespring-loaded or have some other tension adjustment. The enclosure 141may also include an access point, such as a door, as shown in FIG. 6B,which may be used to manually remove trapped solids and/or to access thedoctor blade 162.

In accordance with at least one embodiment, the filter device 100 alsoincludes a backwash system. The backwash system functions to clean thefilter media 118 of the disc filters 117 and the filter surface 112 ofthe rotary drum 110 at periodic or predetermined intervals. A schematicof a backwash system 145 is shown in FIG. 11. The backwash system 145includes a first plurality of spray nozzles 147 that are configured tospray filtrate 122 onto the plurality of filter discs 117. Duringcleaning, the drive assembly 170 turns the filter discs 117 at a lowspeed (e.g., 1-3 rpm) and filtrate 122 or any other backwash fluid ispumped from the outlet trough 135 of the housing 125 (or any othersource of filtrate) to the first plurality of spray nozzles 147 that arepositioned at the top of the disc filters 117. The first plurality ofnozzles 147 functions to clean the filtered solids off the filter media118. The configuration shown in FIG. 11 includes spray nozzles 147 thatare positioned between two adjacent discs 117 such that both sides ofeach disc are sprayed from the “clean” side. The filtrate 122 penetratesthrough the filter media 118 and washes away the collected solids. Adisc filter backwash trough 142 is used to collect the collected solids(particulate matter removed from the filter media 118) and used spraywater (backwashed filtrate), which is collectively referred to herein asbackwash effluent, and transports the backwash effluent out of the discfilter 115, as shown by the arrow in FIG. 11. According to oneembodiment, the disc filter backwash trough 142 (also shown in FIG. 5B)is positioned within the central drum 119 of the disc filter 115.

The backwash system 145 also includes a second plurality of spraynozzles 149 configured spray filtrate 122 onto the filter surface 112 ofthe rotary drum 110. The second plurality of spray nozzles 149 functionsin a similar manner as the first plurality of spray nozzles 147. Thesecond plurality of spray nozzles 149 are also shown in FIG. 6B. Asshown, the second plurality of spray nozzles 149 are disposed on theinterior of the rotary drum 110 and are positioned to spray the “clean”side (first side 114 a) of the filter surface 112. While the rotary drum110 is being rotated (also at a slow speed during backwash), thefiltrate 122 or other backwash fluid is pumped to the second pluralityof spray nozzles 149 and sprayed onto the first side 114 a of the filtersurface 112. The filtrate 122 passes through the filter surface 112 tothe second side 114 b and particulate matter removed from the filtersurface 112 and used spray water is collected in the drum filtercollection trough 140, which transports the backwash effluent out of thedrum filter 105.

According to some embodiments, the first plurality of spray nozzles 147and/or the second plurality of spray nozzles 149 may include one or morefeatures or elements that minimize or reduce clogging. For instance, thespray nozzles may include a retractable element that includes a splitspray tip or other element that is configured to retract into an orificeof the housing of the spray nozzle during non-backwashing operations.When retracted, the split spray tip “splits” outwardly such that debristhat would otherwise clog the orifice of the spray nozzle is released.Once pressurized, the retractable element extends outward from theopening and the split spray tip merges back together to form a spraypattern. Suitable nozzles having these features include the MOMOJet®nozzles available from Ikeuchi USA, Inc.

As shown in FIG. 6B, The second plurality of spray nozzles 149 areangled and positioned such that the outwardly-directed spray patternresults in the backwash effluent being directed into the drum filtercollection trough 140. According to one embodiment, the spray nozzles149 are positioned to be aligned adjacent to one another across thewidth of the rotary drum 110. The spray nozzles 149 may also bepositioned and angled to coincide with the doctor blade 162 such thatthe spray nozzles 149 spray at the filter surface 112 in such a way thatthe doctor blade 162 is more readily able to scrape waste off into thedrum filter collection trough 140. In some instances, the angledorientation of the spray nozzles 149 may be 90 degrees to the filtersurface 112, but in other configurations, the spray nozzles 149 may notbe oriented at 90 degrees. FIG. 7A indicates one potential position forthe spray nozzles 149, and FIG. 7B is an enlarged view of the circledportion of FIG. 7A that indicates the placement and approximate spraydirection. In this instance, the drum filter collection trough 140 ispositioned external to the rotary drum 110, but it is to be appreciatedthat other locations are also within the scope of this disclosure,including the interior of the rotary drum 110.

FIG. 8 is a view of a top portion of the drum filter 105 as installedwithin the housing 125 (the front panel of the housing 125 is shown inFIG. 8). According to various aspects, the drum filter 105 is configuredto be sealed to prevent wastewater 102 from inadvertently entering thedisc filter 115. The embodiment shown in FIG. 8 includes a seal 164,such as a v-ring seal that seals the drum filter 105 to a portion of thehousing 125, and a band clamp 166 to prevent the v-ring seal 164 frommoving. A second sealing mechanism, such as a seal and band clamp, mayalso be positioned on the other side of the drum filter 105 where thecentral drum 119 penetrates through the sealing plate 126, which can beseen in the photograph of FIG. 9). The sealing plate 126, as discussedabove, also prevents the wastewater 102 in the inlet trough 130 fromentering and contaminating the filtrate 122 in the outlet trough 135.FIG. 9 is a photograph of the drum filter 105 attached to the centraldrum 119 of the disc filter 115. The sealing plate 126 is also visiblein FIG. 9.

The size of the drum filter 105 may depend on several factors, includingthe area and opening size of the filter panel 116 of the drum filter 10,and the flow rate of the wastewater for a given head loss.

Referring now to FIG. 12A, a frame support 245 (also referred to hereinas a filter support), for a disc filter 115 in accordance with at leastone embodiment is shown. The frame support 245 serves to support aportion of a side 255 and bottom portion 250 of a pair of filter panels116 (see FIG. 4B). The frame support 245 includes an attachment portion260 and a transversely oriented strut portion 270. The attachmentportion 260 includes a first section 265 which extends from an end 267of the strut portion 270. The attachment portion 260 also includes asecond section 269 which extends from the end 267 in a directionopposite to the first section 265 to thus form an inverted T-shapedframe support 245. The attachment portion 260 further includes a singleaperture 275 which extends along the first 265 and second 269 sectionsof the attachment portion 260 and along the strut portion 270 to thusform a substantially inverted T-shaped aperture which corresponds to theshape of the frame support 245.

Referring to FIG. 12B, the frame support 245 is shown positioned on thecentral drum 119. The attachment portion 260 is designed to bemaintained in alignment with drum aperture 158 such that the aperture275 is in fluid communication or otherwise fluidly connectable with anassociated drum aperture 158 in the central drum 119. The aperture 275is substantially the same size or larger than the drum aperture 158. Inanother embodiment, the frame support 245 is positioned on the centraldrum 119 such that the attachment portion 260 straddles a supportsection of the central drum 119 located in between adjacent drumapertures 158. In this embodiment, portions of two adjacent drumapertures 158 are in fluid communication with the aperture 275.

Referring to FIG. 12C, a pair of filter panels 116 is shown installed inthe frame support 245. The filter panels 116 are spaced apart from eachother. Referring to FIG. 12D in conjunction with FIG. 12E, a side viewof a plurality of frame supports 245 and filter panels 116 is shown. Acap 295 is used to secure each pair of filter panels 116. Each cap 295is removably secured to adjacent radial struts 270 to enable removal ofeach filter panel 116 for cleaning or replacement as necessary. Eachfilter panel pair, frame support 245 and associated cap 295 form afilter panel set 300 for receiving contaminated water. Further, thefilter panels 116, cap 295 and aperture 275 form a volume 182 whosecross sectional area is equal to or larger than the area of drumaperture 158. Volume 182 extends circumferentially around the centraldrum 119 through each filter panel set 300 on the filter disc 117 and iscontinuous. Referring to FIGS. 12B, 12C, and 12D in conjunction withFIG. 12E, the aperture 275 enables fluid communication between the drumaperture 158 and adjacent filter panel sets 300. This enables water andair to flow circumferentially between adjacent filter panel sets 300 asthe central drum 119 rotates, which may increase the capacity of thedisc filter 115.

Referring now to FIG. 13, in accordance with one or more embodiments,the two-stage filtration system 100 may further include one or moresensors 178 (e.g., 178 a and 178 b) and a controller 176, which isoperatively coupled to the one or more sensors 178. The sensors may beconfigured to measure one or more properties of the two-stage filtrationsystem and to send these measurements to the controller 176. Thecontroller 176 may be operatively coupled to one or more components ofthe system 100, such as the drive assembly 170, the backwash system 145,as well as other components, such as pumps and valves (not shown in FIG.13). For instance, the controller 176 may also control one or morevalves or pumps used in the system to control the route of fluidsthrough the system. The controller 176 is configured to receivemeasurements taken by the sensors 178 and to control one or morecomponents of the system, such as the drive assembly 170 and thebackwash system 145.

According to at least one aspect, the system may include a level sensor,such as level sensor 178 a that is positioned in the inlet trough 130 ofthe housing 125 that houses the drum filter 105 and the disc filter 115.The level sensor 178 a may be configured to measure the level ofwastewater 102 (influent water) in the inlet trough 130 of the housing125. An approximate maximum water level (i.e., a predetermined level)for the influent is show in FIG. 7B. Wastewater is fed into the inlettrough 130 at a constant flow rate, which means that the water level inthe inlet trough will increase as the solids build up on the filtersurfaces of the drum filter 105 (i.e., the filter surface 112 becomesmore clogged) and the disc filter 115. The level sensor 178 a may takeperiodic measurements and send these measurements to the controller 176.Therefore, when the water level in the inlet trough 130 exceeds thepredetermined water level (e.g., a water level such as that shown inFIG. 7B), the controller 176 may send one or more signals to the systemthat result in a halt to a filtration process and to start a cleaningprocess. For instance, the controller 176 may control a motor in the thedrive assembly 170 to rotate the drum filter 105 and the disc filter 115at a lower speed and control the sprayers in the backwash system 145 tospray cleaning fluid onto the filter surfaces of each of the drum filter105 and the disc filter 115 as described above.

The one or more sensors may also include one or more parameter sensorsthat are configured to measure other process parameters besides thelevel of influent, which is exemplified at 178 b in FIG. 13. Forinstance, TSS, BOD, chemical oxygen demand (COD), pressure, and/or oneor more flow rates may also be monitored by the controller 176 and usedto control one or more components of the system based on measurementstaken by the one or more parameter sensors.

In accordance with at least one embodiment, a method of treatingwastewater is provided that includes introducing the wastewater (e.g.,102) to a first-stage filtration operation comprising a barrier filter(e.g., 105) to produce filtered wastewater (e.g., 104) and thenintroducing the filtered wastewater to a second-stage filtrationoperation comprising a disc filter (e.g., 115) to produce treated water(e.g., 122). The method can also further include measuring a level ofwastewater introduced to the barrier filter of the first stagefiltration operation and backwashing a filter surface of the barrierfilter based on the measured level of wastewater. In one embodiment, thebarrier filter comprises a rotary drum configured for radially inwardfluid flow and the disc filter is configured for radially outward fluidflow.

EXAMPLES

The following examples further illustrate the invention, and are notintended to limit the scope of the disclosure.

Example 1: Two-Stage Tertiary Filtration with 200 Micron Drum Filter

A pilot plant containing two Forty-X™ filter discs was re-configured toinclude a drum filter as shown in FIG. 14. The drum filter was added tothe influent box (see FIG. 14) that is typically used to measure theinfluent water level as the disc filter captures solids. This locationalso allows for the drum filter to seal off to a plate to preventleaking of influent water to the filtered water. Each disc filter in thepilot plant was 7.2 feet in diameter and included either 10 or 20 micronpleated panel filter media.

A schematic of the placement of the pilot plant within an existingwastewater treatment plant (i.e., test site) is shown in FIG. 15. Thetest site included a secondary treatment process which consisted of anOrbal® biological reactor (Evoqua Water Technologies) followed byTow-Bro® clarifiers (Evoqua Water Technologies) that provided secondaryclarification. The test site also included a tertiary treatment processthat consisted of two Hydrotech™ disc filters (available from Veolia)set up in a parallel configuration. The pilot plant was configured tointake influent originally designated for the second existing discfilter such that effluent from the secondary clarifier was provided asinfluent to the pilot plant, as shown in FIG. 15.

A 200 micron screen was initially installed on the drum filter. The drumfilter was successful in trapping large solids and debris and preventingthese items from entering the disc filter, which was fitted with 10micron filter media. After four months of use, the drum filter showed nosigns of wear. TSS data (see left y-axis of FIG. 16) taken over anapproximate 11-day period from the influent stream (i.e., wastewater102, labeled “influent TSS”) and the effluent of the disc filter (i.e.,122, labeled as “effluent TSS”) is shown in FIG. 16. With an approximateaverage flow rate of about 210 gpm, the influent TSS values ranged from7-22 mg/L and effluent TSS values were, on average, below 5 mg/L. TSSand biochemical oxygen demand (BOD) measurements were also taken of bothreject streams (i.e., solids captured by the drum filter and solidscaptured by the disc filter) and are shown below in Table 1. The resultsfrom this test indicate that the drum filter is able to relieve some ofthe TSS load from the disc filter. For example, both filters removed TSSfrom the wastewater, as indicated in Table 1.

TABLE 1 tertiary reject stream data from 200 micron drum and 10 microndisc filters Drum filter reject stream Disc filter reject stream TSS(mg/L) 220 470 BOD (mg/L) 100 130

Example 2—Two-Stage Tertiary Filtration with 75 Micron Drum Filter

The 200 micron drum filter experiment discussed above in Example 1resulted in minimal head loss across the drum filter in both tertiaryand primary treatment applications (the primary treatment results arediscussed further below). Drum filters having screens with various sizesof openings ranging from 25 microns to 220 microns were tested. Theresults (not shown) from timed draw-down and turbidity tests indicatedthat a 75 micron screen yielded the best results.

A 75 micron filter material was then installed on the drum filter and atwo-stage tertiary filtration process with a 10 micron pleated paneldisc filter was commenced. FIG. 17 includes similar data as shown inFIG. 16 taken over an approximate 24-day period. The flow rate washigher, with values that fluctuated in a range of from about 222 gpm toabout 436 gpm, and the influent TSS values were about the same as inExperiment 1. Again, the effluent TSS values were, on average, below 5mg/L. TSS and BOD measurements were taken of both reject streams and areshown below in Table 2. The results from this test re-confirm that thedrum filter relieves at least a portion of the TSS load from the discfilter. The higher flow rate also yielded a higher concentration ofsolids being trapped by both filters (when compared to the results fromTable 1).

TABLE 2 tertiary reject stream data from 75 micron drum and 10 microndisc filter Drum filter reject stream Disc filter reject stream TSS(mg/L) 1000 890 BOD (mg/L) 170 220

Example 3—Two-Stage Primary Filtration with 200 Micron Drum Filter

For purposes of testing the pilot plant in a primary treatmentapplication, a gas powered trash pump was installed in the raw influentstream that fed the test site. The pump was capable of influent flowrates up to 130 gpm and a secondary pump was used to supplement the flowrate to be as high as 400 gpm.

A 200 micron drum filter was paired with two different sized discfilters. The first disc filter tested was a 10 micron pleated panel discfilter, and two-stage primary filtration was performed using thisconfiguration for approximately 6 days. FIG. 18A is a graph showing theTSS (right y-axis) and BOD (left y-axis) measurement results taken ofthe influent and effluent streams, as well as the flow rate, whichranged from 49 to 98 gpm. The second disc filter that was tested wasfitted with a 25 micron flat stainless steel panel was also tested overan approximate 9-day period. The TSS and BOD measurement results fromthe influent and effluent streams are shown in the graph of FIG. 18B, aswell the flow rate, which ranged from 92 to 415 gpm.

The results shown in FIGS. 18A and 18B indicate an average removal of55% of the influent BOD and 85% of the influent TSS levels. The effluentTSS and BOD values are similar to those achieved without a drum filterfunctioning as a first stage filtration process, but the two-stagefiltration process allows for the disc filter to run more continuouslywithout immediately clogging and having to be taken offline and cleaned.The drum filter as a pre-filter or first stage filtration process alsoincreases the capacity of the system when the influent TSS values arevery high.

Combined influent and effluent TSS data from all three examples are alsoshown in FIG. 17.

Having thus described several aspects of at least one example, it is tobe appreciated that various alterations, modifications, and improvementswill readily occur to those skilled in the art. For instance, examplesdisclosed herein may also be used in other contexts. Such alterations,modifications, and improvements are intended to be part of thisdisclosure, and are intended to be within the scope of the examplesdiscussed herein. Accordingly, the foregoing description and drawingsare by way of example only.

What is claimed is:
 1. A filter device for filtering wastewater, thefilter device comprising: a drum filter including a rotary drum with afilter surface having a first side facing an interior of the drum and asecond side facing an exterior of the rotary drum and being fluidlyconnectable with a source of wastewater; and a disc filter having aninlet fluidly connectable with the first side of the filter surface ofthe rotary drum.
 2. The filter device of claim 1, wherein the discfilter includes a plurality of disc-shaped filter members attached to acentral drum that are configured to receive filtered wastewater passedthrough the filter surface of the drum filter and to filter the filteredwastewater.
 3. The filter device of claim 2, wherein the inlet of thedisc filter is fluidly connectable with an interior of the central drumof the disc filter.
 4. The filter device of claim 2, wherein the rotarydrum of the drum filter and the central drum of the disc filter arepositioned along a common longitudinal axis.
 5. The filter device ofclaim 4, wherein the rotary drum of the drum filter is coupled to thecentral drum of the disc filter.
 6. The filter device of claim 5,further comprising a housing that at least partially surrounds the drumfilter and the disc filter, the housing having an inlet trough fluidlyconnectable with the wastewater and the second side of the filtersurface of the rotary drum filter, an outlet trough fluidly connectablewith filtrate, and a sealing plate configured to separate the inlettrough from the outlet trough.
 7. The filter device of claim 6, furthercomprising a drum filter collection trough fluidly connectable with theexterior of the rotary drum.
 8. The filter device of claim 7, furthercomprising a backwashing system comprising: a first plurality of spraynozzles configured to spray filtrate onto the plurality of disc-shapedfilter members; a disc filter backwash trough configured to collectbackwashed filtrate from the plurality of disc-shaped filter members;and a second plurality of spray nozzles configured to spray filtrateonto the first side of the filter surface of the rotary drum, whereinthe drum filter collection trough is configured to collect backwash fromthe filter surface of the rotary drum.
 9. The filter device of claim 1,wherein the filter surface of the rotary drum is configured to retainsolids on the second side while permitting the wastewater to filterthrough the filter material to the first side of the filter material andthe interior of the rotary drum as filtered wastewater.
 10. The filterdevice of claim 1, wherein the filter surface of the drum filter hasopenings with a diameter in a range of about 20 microns to about 800microns.
 11. The filter device of claim 10, wherein the filter surfaceof the drum filter comprises one of wedge wire screen material or wovenfilter media material.
 12. The filter device of claim 10, wherein theplurality of disc-shaped filter members include a filter media withopenings having a diameter in a range of about 6 microns to about 300microns.
 13. The filter device of claim 1, wherein the wastewater isfrom one of a secondary or primary treatment process.
 14. A two-stagefiltration system for filtering wastewater, the system comprising: aninlet fluidly connectable with the wastewater; a first stage filterassembly fluidly connectable with the inlet and having a rotary drumwith a filter surface configured for radially inward fluid flow; asecond stage filter assembly fluidly connectable with the first stagefilter assembly and having a plurality of filter discs configured forradially outward fluid flow; and an outlet fluidly connectable withfiltrate generated by the second stage filter assembly.
 15. Thetwo-stage filtration system of claim 14, wherein the plurality of filterdiscs are attached to a central drum that is fluidly connectable with aninterior of the rotary drum of the first stage filter assembly.
 16. Thetwo-stage filtration system of claim 14, wherein the first stage filterassembly and the second stage filter assembly are rotatable around acommon longitudinal axis, and the system further comprises a driveassembly coupled to the first stage filter assembly and the second stagefilter assembly.
 17. The two-stage filtration system of claim 16,further comprising a backwashing system having a first plurality ofspray nozzles configured to spray the filtrate onto the plurality offilter discs and a second plurality of spray nozzles configured to spraythe filtrate onto an inwardly facing side of the filter surface of therotary drum.
 18. The two-stage filtration system of claim 17, furthercomprising a level sensor configured to provide measurements of a levelof wastewater provided by the inlet to the first stage filter assembly.19. The two-stage filtration system of claim 18, further comprising acontroller operatively coupled to the level sensor, the drive assembly,and the backwashing system, the controller configured to control atleast one of the drive assembly and the backwashing system based onmeasurements from the level sensor.
 20. The two-stage filtration systemof claim 14, wherein the filter surface of the drum filter has openingswith a diameter in a range of about 20 microns to about 800 microns. 21.The two-stage filtration system of claim 20, wherein the filter discsinclude a filter media with openings having a diameter in a range ofabout 6 microns to about 300 microns.
 22. The two-stage filtrationsystem of claim 14, wherein the inlet is fluidly connectable with asecondary clarifier of a secondary treatment process.
 23. The two-stagefiltration system of claim 14, wherein the inlet is fluidly connectablewith influent to a primary treatment process.
 24. The two-stagefiltration system of claim 14, wherein the second stage disc filterassembly comprises: a central drum configured to receive filteredwastewater from the first stage filter assembly, the central drumincluding a plurality of drum apertures; a frame comprising a pluralityof frame supports each having an attachment portion coupled to thecentral drum and a radial strut portion extending from the attachmentportion, each of the plurality of frame supports defining a single frameaperture that extends through the attachment portion and along an entirelength of the radial strut portion to correspond with the shape of theframe support; and a plurality of adjacent filter segments positionedaround the central drum, each of the plurality of adjacent filtersegments defining a cavity in fluid communication with at least one ofthe plurality of drum apertures and supported at a first side by a firstframe support and at a second side by a second frame support, theplurality of frame apertures and cavities arranged to form acircumferential open fluid channel extending continuously around thecentral drum to enable the filtered wastewater to pass substantiallyunimpeded through the plurality of drum apertures and through theplurality of adjacent filter segments.
 25. The two-stage filtrationsystem of claim 24, wherein the single frame aperture forms an invertedsubstantially T-shaped configuration.
 26. A method of treatingwastewater, comprising: introducing the wastewater to a first-stagefiltration operation comprising a barrier filter to produce filteredwastewater; and introducing the filtered wastewater to a second-stagefiltration operation comprising a disc filter to produce treated water.27. The method of claim 26, further comprising measuring a level of thewastewater introduced to the barrier filter of the first stagefiltration operation.
 28. The method of claim 27, further comprisingbackwashing a filter surface of the barrier filter based on the measuredlevel of wastewater.
 29. The method of claim 26, wherein the barrierfilter comprises a rotary drum configured for radially inward fluidflow.
 30. The method of claim 29, wherein the disc filter is configuredfor radially outward fluid flow.